Problem: Tiffany ate 2 slices of pizza. Michael ate 1 slice. If Tiffany ate $\dfrac{2}{7}$ of the pizza, what fraction of the pizza is remaining?
Explanation: If 2 slices represent $\dfrac{2}{7}$ of the pizza, there must have been a total of 7 slices. $\text{fraction of pizza remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 3 slices, which leaves 4 out of 7 slices remaining. There is $\dfrac{4}{7}$ of the pizza remaining.